Aryl Glyoximes

A quick perusal of Table 3 shows inverted stability for a and /3 isomers of phenyl-glyoxime and p-tolylglyoxime. Given uncertainties as to stereochemistry it is plausible that the structural assignments of Z and E, syn and anti, even a and /3 were reversed. This is understandable. However, it is inexplicable that the tolyl species have enthalpies of formation at least 150 kJ moH more positive than the phenyl compounds. This is an altogether implausible result. The solid phase reaction 35 is calculated to be ca 75 kJmol exothermic if we use the averaged value for the various stereoisomers of phenylglyoxime and benzil dioxime. This, too, is implausible. 

We can only conclude that these aryl glyoxime data are suspect. As such, although we finally have data for sets of enthalpies of formation of syn- and awft -isomers, we do not trust these data enough to return to the earlier question of the relative stabilities of these isomers as enunciated in the discussion of monooximes. 

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The glyoxime dehydration route is compatible with various substituents including not only alkyl, aryl, and heteroaryl but also acyl, carboxyl, and amino groups for example, 3-amino-4-phenylfurazan is formed on heating a-(hydroxyimino)phenylacetamidoxime with sodium acetate in ethanol, and the same compound also results from treatment of benzoyl cyanide with hydroxylamine and sodium acetate in ethanol <87IJC(B)690>. 

The complexes with unsubstituted and either alkyl- or aryl-substituted glyoximes have been prepared by the reaction of nickel(II) salts with the appropriate ligand in aqueous or ethanolic solution or an aqueous-ethanolic mixture. In most cases, the reaction is promoted by addition of ammonia as base and/or refluxing temperature. 

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